Since the discovery of ferrocene in 1951, a number of metallocenes have been prepared by the combination of compounds prepared from cyclopentadiene-type compounds and various transition metals. The term "cyclopentadiene-type compounds" as used herein refers to compounds containing the cyclopentadiene structure. Examples include unsubstituted cyclopentadiene, unsubstituted indene, unsubstituted fluorene, and substituted varieties of such compounds. Also included is tetrahydroindene.
Many of the cyclopentadiene-type metallocenes have been found useful in catalyst systems for the polymerization of olefins. It has been noted in the art that variations in the chemical structure of such cyclopentadienyl-type metallocenes can have significant effects upon the suitability of the metallocene as a polymerization catalyst. For example, the size and location of substitutions on cyclopentadienyl-type ligands has been found to affect the activity of the catalyst, the stereoselectivity of the catalyst, the stability of the catalyst, or various properties of the resulting polymer; however, the effects of various substituents is still largely an empirical matter, that is, experiments must be conducted in order to determine just what effect a particular variation in the chemical structure of the metallocene will have upon its behavior as a polymerization catalyst.
While there are references in the prior art which contain broad general formulas that encompass a vast number of unbridged metallocenes, it is considered unlikely that all of the metallocenes within the broad disclosures of publications have actually been prepared and evaluated for their polymerization effects. For example, while U.S. Pat. Nos. 5,049,535; 5,225,092; and 5,126,303 and WO 94/11406 contain allegations regarding a wide range of both bridged and unbridged metallocenes, the only actual examples of unbridged metallocenes are those in which two identical cyclopentadienyl-type ligands are present, i.e. symmetrical unbridged metallocenes. Similarly, while U.S. Pat. No. 5,331,054 names two unsymmetrical unbridged metallocenes, viz. (cyclopentadienyl) (indenyl) and (cyclopentadienyl) (fluorenyl) zirconium dichlorides, those compounds do not contain substituted indenyl groups and again the actual examples used symmetrical unbridged metallocenes. While published EPC application 685,485 discloses unsymmetrical unbridged metallocenes containing substituted indenyl groups, the metallocenes also contain a pentamethylcyclopentadienyl group. Similarly, while U.S. Pat. No. 5,223,467 proposes unsymmetrical unbridged metallocenes which could include substituted indenyl groups it also specifies that the other cyclopentadienyl ring also be substituted and it does not contain any actual examples having an indenyl ligand.
Many of the unbridged metallocenes have been found not to be sufficiently active in the polymerization of olefins to be of significant commercial interest. The aforementioned EPC 685,485 reveals that indenyl pentamethylcyclopentadienyl Zr dichloride is much more active than indenyl cyclopentadienyl, which in turn is much more active than either the bis indenyl or bis cyclopentadienyl counterparts. Prior to the present applicants' work there does not appear to have been any work which suggests what effect substituents on indenyl would have on an unsymmetrical unbridged (indenyl) (unsubstituted cyclopentadienyl) metallocene.
An object of the present invention is to provide certain new substituted indenyl-containing metallocenes. Still another object of the present invention is to provide polymerization catalyst systems employing the specific indenyl-type metallocenes. Still yet another object of the present invention is to provide processes for the polymerization of olefins using specific indenyl-type metallocene catalyst systems. Yet another object of the present invention is to provide catalyst systems which provide unusually high activity or molecular weight in the polymerization of olefins.